Spark plug



L. McK'. FIELD SPARK PLUG Nov. 22, 1949 Filed April 7, 1947 Qvwwwtov LLOYD M. F/ELD Patented Nov. 22, 1949 UNITED STATES PATENT OFFICE 3 Claims.

10,000 miles of operation, in order to maintain high efficiency and save fuel. The loss of efficiency is usually due to enlarging of the gap between adjustments, and because it is more diflicult to make proper adjustments as the points are more badly worn'away and burnt. Thus, the combustion of the fuel charges in the engine cylinders becomes less complete because of poor or faulty ignition, and this becomes evident in a higher fuel consumption per mile.

If high eificiency is to be maintained, therefore, the spark plugs have to be discarded every 10,000 miles or so. Their life may be prolonged at some sacrifice in efficiency for another ten or twenty thousand miles, but ultimately they wear out to the extent that they become entirely inoperative and have to be replaced, even though the only parts that are defective are the gap forming elements, which are the positive and neg ative electrode tips.

The object of the present invention is to devise a spark plug with a novel arrangement of the electrodes, whereby the negative, or both electrodes, may readily be replaced by anyone without any special tools, and at small expense, so as to prolong the life of the main portion of the spark plug indefinitely, and retain high efficiency of operation at a relatively smaller cost than was heretofore possible.

Another object is to modify the construction of the conventional spark plug, having a positive central electrode, by providing a removably attachable negative electrode, which may readily be replaced by a new one when worn out.

Another object is to provide a spark plug, having a threaded engagement with the engine cylinder, with a replaceable negative electrode having a leg with a projection at its end, and a corresponding groove in the threaded surface of the spark plug for the leg to fit in, with a snug fit, and to project from, sufficiently to be caught by the internal thread in the engine cylinder opening, as the plug is threaded into place on the engine, so that a good electrical as well as heat transfer contact is obtained for the electrode in operation.

Another object is to make the groove, above referred to, extend from the end of the threaded surface for a short distance at a depth slightly less than the thickness of the leg under the base of the thread, and then radially inwardly to form a shoulder, and to make the projection on said leg extend inwardly to fit over said shoulder to form a rigid structure with said spark plug when the negative electrode is pressed into the groove.

Another object is to make a groove as defined above on each side of said spark plug, and form the negative electrode in the shape of a U with a pair of legs for straddling the threaded portion of the spark plug, each leg snugly fitting into one of said grooves to form a more rigid structure.

Another object is to make the groove, above referred to, extend the same depth throughout, but having a portion extending circumferentially across the axial portion, and make the projection of the leg correspondingly extend normally to its axial portion so as to fit snugly in the groove and form a rigid structure with the spark plug when pressed into place in said groove.

Another object is to make a groove as defined above on each side of said spark plug, and form the negative electrode in the shape of a U with a pair of legs for straddling the threaded portion of the spark plug, each leg snugly fitting into one of said grooves to form a more rigid structure therewith.

Another object is to adapt any of the negative electrode constructions defined above to a spark plug having a replaceable positive electrode, such as is disclosed in my prior Patent No. 2,371,162.

Other and more specific objects will become apparent in the following detailed description of spark plugs illustrating the present invention, having reference to the accompanying drawings, wherein:

Figure 1 is an elevational view of one form of spark plugs having a conventional central positive electrode and a removable U-shaped negative or grounded electrode in accordance with the present invention,

Figure 2 is a sectional view thereof, taken on the line 22 of Figure 1, showing the plug mounted in a jacketed engine cylinder,

Figure 3 is a cross-section taken on the line 3-3 of Figure 1,

Figures 4 and 5 are two views of a replaceable 3 negative electrode that may be used with the above spark plug,

Figure 6 is a partial sectional view of another form of spark plug body constructed in accordance with this invention,

Figure 7 is a negative electrode for use in connection with this form of spark plug,

Figure 8 is a partial sectional view of a spark plug having a removable central electrode tip of the type disclosed in my prior patent above referred to, and a U-shaped removable negative electrode,

Figure 9 is a partial sectional view of the spark plug of the type disclosed in said prior patent, and

Figure 10 is a partial sectional'view of the same spark plug, showing how the negative electrode might be distorted due to overheated and/ or continual tapping of the free positive electrode tip thereagainst during operation.

Similar parts in the several views of the drawing aredesignated by the same numerals.

In Figures 1,2, 3 and 6, a conventional plug of the type having a central positive electrode l, fixed in an insulated core 2, has a body 3, the threaded portion 1 of which has been modified by grooving'on opposite sides. In Figures l to 3 this groove is in the form of a T, the stem portion 5 of which extends axially from the end of the thread for a short distance to the portion 5 at right angles thereto, the portion 6 extending circumferentially and being of the same depth as theportion 5.

A removable -U-shaped electrode 1 having its T-shaped legs '8 made to fit snugly in these groovesand to fill them to a depth slightly above the base of the threads 4, is mounted as shown by pressing the ends of the cross bar portion -9. of thelegs to fit snugly into the portion '6 of the groove. Notches id may be provided, leading into the grooves, as showrnior insertion of any pointed instrument behind the legs of the electrode to facilitate removal thereof from the grooves, when it' is desired to replace the electrode.

Figure 2 shows this plugmounted in place in the threaded spark plug hole of an engine cylinder 1' I, having-a water jacket. A gasket 52 is interposed between a Wall of the spark plug body 3 and-the engine cylinder H. It will be seen that dueto the legs filling the grooves to a depth slightly above the base of'the threads 4, the legs are subjected to pressure by the threadsin the threaded spark plug'hole, to provide a good electrical ground-for the negative electrode as well as a good heat transfer path for direct coolingof the negative electrode by the cylinder cooling means, whether it be watercooling, such as shown, or air-cooling, as in air-cooled engines. The usual spark plug gasket is shown at 12, and the high tension or positive electrode terminal at l5.

Figure 3 shows how the cross bar portion 9 is pressed around th groove portion- 6 so that its ends or ears fit snugly'against the bottom and sides of the groove. When the electrode is pressed into place in the groove so as to form a rigid structure with the body of the spark plug, the gap is adjusted for proper clearance with the end of the positive electrode I, before the spark plug is placed in the engine cylinder for operation. The adjustment may be done in any suitable manner by bending the part of the nega tive electrode 1 between its legs toward or away from the ends of electrode i. Electrode l is designed so that it will require very little, if any, bending to obtain proper clearance.

It may be designed so as to normally require some inward bending as shown in the form 1 illustrated in Figures 4 and 5. This form is conducive to more resistance against distortion under extreme conditions of operation, due to the greater strength provided by the arched shape of the cross piece between the legs 8.

Figure 6 and '7 show parts of a modified form of spark plug threaded portion 4', wherein the groove 5 at its upper end extends radially inwardly, to form a radial shoulder or looking groove 6', instead of the circumferential portion 6 of the form illustrated in Figures 1 to 3. The

U-shaped negative electrode 1" has corresponding legs 8' with its ends 9' turned inwardly to fit into these radially inwardly extending portions 6' of the grooves.

Notches similar to H! may be provided in this form of plug to facilitate extricating these electrodes in like fashion. The depth of the grooves and the thickness of the legs 8'of these electrodes-are related in :the sameway as in the first f0rm,-so astoprovide good contact over extended surfaces between the parts, when the plug is mounted in its threaded hole in the engine cylinder, for proper ground and maximum coefficient of heat transfer.

The form of negative electrode 1 shown in Figures 4 and 5 is shown applied to a-spark plug of the type having aremovable center electrode tip I in Figure 8, and is thus an improvement over this type of plug, one form of which is disclosed in my prior patent and illustrated in partial views-in Figures'9 and i the drawing in the present application. This plug wasdescribed as having a fluid inlet through the stem l3 of the center electrode'for the introduction of head lubricant into theengine cylinder, and the end of the electrode was made separate from the stem and mounted-loosely in the end of the insulator core 2, to form a valve, opening and closing the fluid inlet automatically in response to the changing pressures in the engine cylinder, alternately feeding the lubricant thereinto and forming a gap with the negative electrode -l4, which was of the fixed, non-replaceable type. Thus, although this plug construction had certain definite advantages over previous types, it had a fixed negative electrode which had some tendency to distort, as shown in Figure 10, under extreme temperature conditions, due to .the continuous tapping of the positive electrode ti I against it, in operation. Furthermore, in order to replace the center electrode tip, it was necessary to bend the negative electrode l4 out of its way, and then back to a properly adjusted-position after installation of the-new-tip I. This would cause weakening of the electrode at the bent portion, and in time i the electrode would break, causing the spark plug to be useless.

The modification of this plug by incorporation of the removable-electrode 'i", as shown in- Figure 8, e marked improvement, in that no longer is it necessary to throw away the whole plug when the electrodes fail. All that is required is to replace-the defective electrode by a new one, the cost of which is negligible by comparison; and the life offla spark plug may be extended indeffinitely, since the otherparts of the plug do not normally wear out.

The modification illustrated in Figure 8 may be provided with notches similar to those shown at loin Figures 1 and 2 to facilitate removal of the negative electrode, if desired.

Manyobvious modifications may *bemade-in the iormand arrangement of partsdn the devices described above without departing from the spirit and scope of this invention, as defined in the appended claims.

What is claimed is:

1. A spark plug having a recess in its threaded portion with the upper end of the recess terminating below the upper end of the threaded portion, a removable negative electrode having a leg formed to interlock with said recess by means of a press fit, said leg being thicker than the depth of said recess below the base of the threads of said threaded portion, whereby said threads will be chased across it by the female thread, when said plug is screwed into its threaded opening in an engine cylinder to provide a good electrical as well as heat transfer contact for said electrode in operation.

2. A spark plug having a pair of recesses on opposite sides of its threaded portion with the upper ends of the recesses terminating below the upper end of the threaded portion, a removable negative electrode extending across the end of the plug and having a pair of legs at its ends, formed to interlock with said recesses by means of a press fit, each of said legs being thicker than the depth of each recess below the base of the threads of said threaded portion, whereby said threads will be chased across it by the female thread, when said plug is screwed into its threaded opening in an engine cylinder to provide a good electrical and heat transfer contact for said electrode in operation.

3. A spark plug having a conventional center electrode and a threaded body, grooves in opposite sides of the threaded portion of said body with the upper ends of the grooves terminating below the upper end of the threaded portion, a U-shaped ground electrode having its legs straddling said threaded portion and removably fitted in said grooves, with a snug fit to provide a good heat conducting contact with said body, the outer surface of said legs extending in a cylindrical plane sufficiently above the depth of the base of the threads of said threaded portion to be caught and grooved by the female thread, when said plug is screwed into its threaded opening in an engine cylinder, thereby to provide a good electrical as well as heat transfer contact for said electrode in operation.

LLOYD McKlNSEY FIELD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,247,102 Forbes Nov. 20, 1917 1,643,770 Jacobs Nov. 8, 1927 2,095,540 Blood Oct. 12, 1937 2,371,162 Field Mar. 13, 1945 

